1. Field of the Invention
The invention relates to a method for controlling a spin cycle, including clothes load distribution and liquid extraction, in an automatic washing machine.
2. Description of the Related Art
Top and front loading horizontal axis washing machines are well known appliances for cleaning clothing and other fabric items, such as sheets, towels, and the like. Typically, the fabric items in the load are subjected to a cleaning cycle comprising a wash cycle, a rinse cycle, and a spin cycle for extracting rinse liquid from the load. During the spin cycle, a basket that holds the load rotates relative to a coaxial, imperforate drum to impart centrifugal forces on the load. The basket rotates at a high extraction speed sufficient to “plaster” the load to the peripheral wall of the basket (the clothes rotate with the basket and do not tumble) and extract liquid from the fabric items. Generally, the faster the rotation speed, the greater the amount of liquid that can be extracted. This process is effective at removing excess liquid from the fabric items to prepare them to be line dried or dried in a clothes dryer.
A common problem associated with spin cycles is uneven distribution of the load, which is commonly referred to as an imbalanced load. When the fabric items are not evenly distributed in the basket while rotating at the extraction speed, the basket vibrates. Small vibrations can be tolerated and dampened through a suspension system operatively coupled to the basket, but large vibrations tend to generate annoying noise and can damage the washing machine. Most washing machines have a balance condition monitor comprising sensors positioned adjacent the basket or utilizing internal indicators, such as motor current or speed, for identifying when the load is imbalanced. If the imbalance in the load as detected by the balance condition monitor exceeds a predetermined limit, then the washing machine attempts to remedy the imbalance by redistributing the load or ceases rotation of the basket for manual redistribution of the load by the user.
To avoid imbalances in the clothes load at the extraction speed, the washing machine can attempt to distribute the fabric items evenly over the peripheral wall of the basket prior to rotating the basket at the extraction speed. While the imbalance condition is a problem for both vertical and horizontal axis washing machines, the problem is more serious for horizontal axis machines because of their much greater extraction speeds and the tendency of the clothes load to locate on one side of the basket because of gravity.
Numerous methods of distributing the clothes load have been developed for horizontal axis washing machines. Oftentimes, a system for detecting load imbalance is employed during the distribution step so that the washing machine can respond if a load imbalance is detected during or after distribution. However, some distribution methods are reactive in that they attempt to distribute the load and check for load imbalance thereafter rather than being proactive by monitoring load imbalance as the load is distributed and taking action to remedy the imbalance once it is detected. Reactive distribution methods can be extremely inefficient, especially if the load is not properly distributed in the initial attempts. Additionally, most distribution methods do not consider the size of the clothes load and are, therefore, unnecessarily long, especially for relatively small clothes loads. All other things being equal, a shorter cycle time is always preferred by the consumer. Thus, it is desirable for a washing machine to efficiently distribute a load according to its size during a spin cycle and redistribute the load if the fabric items in the load become unbalanced during the spin cycle.